Multi-mode rfid tag architecture

ABSTRACT

A multi-mode RFID tag includes a power generating and signal detection module, a baseband processing module, a transmit section, a configurable coupling circuit, and an antenna section. In near field mode, the configurable coupling circuit is operable to couple the transmit section to a coil or inductor in the configurable coupling circuit to transmit an outbound transmit signal using electromagnetic or inductive coupling to an RFID reader. In far field mode, the configurable coupling circuit is operable to couple the transmit section to the antenna section, and the multi-mode RFID tag then utilizes a back-scattering RF technology to transmit the outbound transmit signal to RFID readers.

CROSS REFERENCE TO RELATED PATENTS

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. §120, as a continuation, to U.S. Utility application Ser. No.11/928,544, entitled “Multi-Mode RFID Tag Architecture,” (AttorneyDocket No. BP6584), filed Oct. 30, 2007, pending, which claims prioritypursuant to 35 U.S.C. §119(e) to the following U.S. Provisional PatentApplications which are hereby incorporated herein by reference in theirentirety and made part of the present U.S. Utility Patent Applicationfor all purposes:

-   -   a. U.S. Provisional Application Ser. No. 60/921,221, entitled        “RFID System,” (Attorney Docket No. BP6250), filed Mar. 30,        2007, expired; and    -   b. U.S. Provisional Application Ser. No. 60/932,411, entitled        “RFID System”, (Attorney Docket No. BP6250.1), filed May 31,        2007, expired.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to communication systems and moreparticularly to RFID systems.

2. Description of Related Art

A radio frequency identification (RFID) system generally includes areader, also known as an interrogator, and a remote tag, also known as atransponder. Each tag stores identification or other data for use inidentifying a person, item, pallet or other object or data related to acharacteristic of a person, item, pallet or other object. RFID systemsmay use active tags that include an internal power source, such as abattery, and/or passive tags that do not contain an internal powersource, but instead are remotely powered by the reader.

Communication between the reader and the remote tag is enabled by radiofrequency (RF) signals. In general, to access the identification datastored on an RFID tag, the RFID reader generates a modulated RFinterrogation signal designed to evoke a modulated RF response from atag. The RF response from the tag includes the coded data stored in theRFID tag. The RFID reader decodes the coded data to identify ordetermine the characteristics of a person, item, pallet or other objectassociated with the RFID tag. For passive tags without a battery orother power source, the RFID reader also generates an unmodulated,continuous wave (CW) signal to activate and power the tag during datatransfer. Thus, passive tags obtain power from transmissions of the RFIDreader. Active tags include a battery and have greater ability to powertransceivers, processer, memory and other on-tag devices.

RFID systems typically employ either far field or near field technology.In far field technology, the distance between the reader and the tag isgreat compared to the wavelength of the carrier signal. Typically, farfield technology uses carrier signals in the ultra high frequency ormicrowave frequency ranges. In far-field applications, the RFID readergenerates and transmits an RF signal via an antenna to all tags withinrange of the antenna. One or more of the tags that receive the RF signalresponds to the reader using a backscattering technique in which thetags modulate and reflect the received RF signal.

In near-field technology, the operating distance is usually less thanone wavelength of the carrier signal. Thus, the reading range isapproximately limited to 20 cm or less depending on the frequency. Innear field applications, the RFID reader and tag communicate viaelectromagnetic or inductive coupling between the coils of the readerand the tag. Typically, the near field technology uses carrier signalsin the low frequency range. For the tag coil antennas, RFID tags haveused a multilayer coil (e.g., 3 layers of 100-150 turns each) wrappedaround a metal core at lower frequencies of 135 KHz. Sometimes, athigher frequency of 13.56 MHz, RFID tags have used a planar spiral coilinductor with 5-7 turns over a credit-card-sized form factor. Such tagcoil antennas are large in comparison to the other modules of the RFIDtag and are not able to be integrated on a chip, such as a complementarymetal-oxide-semiconductor (CMOS), bipolar complementarymetal-oxide-semiconductor (BiCMOS) or gallium arsenide (GaAs) integratedcircuit, with other modules of the RFID tag.

The International Organization for Standardization (ISO) has developedan RFID standard called the ISO 18000 series. The ISO 18000 seriesstandard describes air interface protocols for RFID systems especiallyin applications used to track items in a supply chain. The ISO 18000series has seven parts to cover the major frequencies used in RFIDsystems around the world. The seven parts are:

-   -   18000-1: Generic parameters for air interfaces for globally        accepted frequencies;    -   18000-2: Air interface for below 135 KHz;    -   18000-3: Air interface for 13.56 MHz;    -   18000-4: Air interface for 2.45 GHz;    -   18000-5: Air interface for 5.8 GHz;    -   18000-6: Air interface for 860 MHz to 930 MHz;    -   18000-7: Air interface at 433.92 MHz.

According to the ISO 18000-2 and 18000-3 parts of the ISO 18000 series,near-field technology with magnetic/inductive coupling has an airinterface protocol at low frequency (LF) of 135 KHz or less or at 13.56high frequency (HF). ISO 18000-3 defines two modes. In mode 1, the tagto reader data rate is 26.48 kbps while mode 2 is a high speed interfaceof 105.9375 kbps on each of 8 channels. The communication protocol usedby the reader and the tag is typically a load modulation technique.

Far field technology with RF backscatter coupling has three ISO definedair interfaces at 2.45 GHz microwave frequency according to ISO 18000-5,860 MHZ to 930 MHz ultra high frequency (UHF) range according to ISO18000-6 and 433.92 MHz UHF according to ISO 18000-7. For UHF at 860-930MHz, the ISO 18000-6 has defined two tag types, Type A and Type B with atag to reader link defined as including 40 kbps data rate, AmplitudeShift Keying (ASK) modulation, and biphase-space or FM0 encoding ofdata.

In addition, the EPCglobal Class 1, Generation 2 standard defines a tagstandard using UHF with a tag to reader link of 40 to 640 kbps, ASK orPhase Shift Keying (PSK) modulation and data encoding of FM0 orMiller-modulated subcarrier.

Generally, tags employing near field technology operating at LF or HFhave been used in applications involving item-level tagging forinventory control in the supply chain management or applicationsinvolving short range reads such as smart cards or vicinity creditcards, e.g. for access control or monetary use, passports, money billsauthentication, bank documents, etc. Such applications do not need longrange reads of the tags but may need more security provided by nearfield technology. In addition, near field technology is known for betterperformance on tags near fluids, such as fluid medications, wherein farfield RF coupling tends to incur interference from the fluids.

Tags employing far field technology RF coupling at microwave or UHF havebeen used in applications involving shipping units such as pallets orcarton level tracking or other applications needing long-distance reads.

These different types of technology and the number of different RFIDstandards, each defining a different protocol for enabling communicationbetween the reader and the tag, has inhibited the wide spread use ofRFID tags for multiple applications. Therefore, a need exists for ahighly integrated, low-cost RFID tag. In addition, a need exists for amulti-standard, multi-technology RFID tag.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theDrawings, the Detailed Description of the Invention, and the claims.Other features and advantages of the present invention will becomeapparent from the following detailed description of the invention madewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of an RFID systemin accordance with the present invention;

FIG. 2 is a schematic block diagram of an embodiment of a multi-modeRFID tag in accordance with the present invention;

FIG. 3 is a schematic block diagram of a configurable coupling circuitin one embodiment of a multimode RFID tag in accordance with the presentinvention;

FIG. 4 is a schematic block diagram of another embodiment of a multimodeRFID tag in accordance with the present invention;

FIG. 5 is a schematic block diagram of coil antennas in one embodimentof a multimode RFID tag and RFID reader in accordance with the presentinvention; and

FIG. 6 is a schematic block diagram of magnetic coupling between amulti-mode RFID tag and RFID reader in one embodiment in accordance withthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 is a schematic block diagram of an RFID (radio frequencyidentification) system that includes a computer/server 12, a pluralityof RFID readers 14-18 and a plurality of RFID tags 20-30. The RFID tags20-30 may each be associated with a particular object for a variety ofpurposes including, but not limited to, tracking inventory, trackingstatus, location determination, assembly progress, et cetera. The RFIDtags may be active devices that include internal power sources orpassive devices that derive power from the RFID readers 14-18.

Each RFID reader 14-18 wirelessly communicates with one or more RFIDtags 20-30 within its coverage area. For example, RFID tags 20 and 22may be within the coverage area of RFID reader 14, RFID tags 24 and 26may be within the coverage area of RFID reader 16, and RFID tags 28 and30 may be within the coverage area of RFID reader 18. In one mode ofoperation, the RF communication scheme between the RFID readers 14-18and RFID tags 20-30 is a backscatter coupling technique using far fieldtechnology whereby the RFID readers 14-18 request data from the RFIDtags 20-30 via an RF signal, and the RF tags 20-30 respond with therequested data by modulating and backscattering the RF signal providedby the RFID readers 14-18. In another mode of operation, the RFcommunication scheme between the RFID readers 14-18 and RFID tags 20-30is a magnetic or inductive coupling technique using near fieldtechnology whereby the RFID readers 14-18 magnetically or inductivelycouple to the RFID tags 20-30 to access the data on the RFID tags 20-30.Thus, in one embodiment of the current invention, the RFID tags 20-30may communicate in a far field mode to an RFID reader 14-18 with suchcapabilities and in a near field mode to an RFID reader 14-18 with suchcapabilities.

The RFID readers 14-18 collect data as may be requested from thecomputer/server 12 from each of the RFID tags 20-30 within its coveragearea. The collected data is then conveyed to computer/server 12 via thewired or wireless connection 32 and/or via peer-to-peer communication34. In addition, and/or in the alternative, the computer/server 12 mayprovide data to one or more of the RFID tags 20-30 via the associatedRFID reader 14-18. Such downloaded information is application dependentand may vary greatly. Upon receiving the downloaded data, the RFID tag20-30 can store the data in a non-volatile memory therein.

As indicated above, the RFID readers 14-18 may optionally communicate ona peer-to-peer basis such that each RFID reader does not need a separatewired or wireless connection 32 to the computer/server 12. For example,RFID reader 14 and RFID reader 16 may communicate on a peer-to-peerbasis utilizing a back scatter technique, a wireless LAN technique,and/or any other wireless communication technique. In this instance,RFID reader 16 may not include a wired or wireless connection 32 tocomputer/server 12. In embodiments in which communications between RFIDreader 16 and computer/server 12 are conveyed through the wired orwireless connection 32, the wired or wireless connection 32 may utilizeany one of a plurality of wired standards (e.g., Ethernet, fire wire, etcetera) and/or wireless communication standards (e.g., IEEE 802.11x,Bluetooth, et cetera).

As one of ordinary skill in the art will appreciate, the RFID system ofFIG. 1 may be expanded to include a multitude of RFID readers 14-18distributed throughout a desired location (for example, a building,office site, et cetera) where the RFID tags may be associated withaccess cards, smart cards, mobile phones, personal digital assistants,laptops, personal computers, inventory items, pallets, cartons,equipment, personnel, et cetera. In addition, it should be noted thatthe computer/server 12 may be coupled to another server and/or networkconnection to provide wide area network coverage.

FIG. 2 is a schematic block diagram of an embodiment of a multi-modeRFID tag 38 which can be used as one of the RFID tags 20-30 in FIG. 1.The multi-mode RFID tag 38 is operable to communicate in a far fieldmode to an RFID reader 14-18 and in a near field mode to an RFID reader14-18. The multi-mode RFID tag 38 includes a power generating and signaldetection module 40, a baseband processing module 42, a transmit section44, a configurable coupling circuit 46, and an antenna section 48. Themulti-mode RFID tag 38 may be an active tag and include a battery 41. Ifan active tag, the battery 41 may replace or assist the power generatingfunction of the power generating and signal detection module 40 to powerthe baseband processing module 42, transmit section 44 and configurablecoupling circuit 46. If the multi-mode RFID tag 38 is a passive tag, nobattery 41 is present.

The power generating and signal detection module 40, baseband processingmodule 42 and transmit section 44 may be a single processing device or aplurality of processing devices. Such a processing device may be amicroprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on hard coding of the circuitry and/oroperational instructions. One or more of the modules may have anassociated memory element, which may be a single memory device, aplurality of memory devices, and/or embedded circuitry of the module.Such a memory device may be a read-only memory, random access memory,volatile memory, non-volatile memory, static memory, dynamic memory,flash memory, cache memory, and/or any device that stores digitalinformation. Note that when the module implements one or more of itsfunctions via a state machine, analog circuitry, digital circuitry,and/or logic circuitry, the memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Further note that, the memory elementstores, and the module executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in FIGS. 1-7.

In an embodiment, the antenna section 48 is a dipole type antennaoperable at microwave or UHF ranges. Folded dipoles or half-wave dipolescan be used or other dipole type antennas that can be bent or meanderedwith capacitive tip-loading or bowtie-like broadband structures are alsoused for compact applications. In general, the antenna section 48 can beone of several types of antennas optimized for the desired frequency ofoperation and application.

In operation, the configurable coupling circuit 46 is operable to couplethe power generating and signal detection module 40 to the antennasection 48 in a far field mode or to couple the power generating andsignal detection module 40 to an inductor or coil antenna in theconfigurable coupling circuit 46 in a near field mode, as explained inmore detail below. In either mode, the configurable coupling circuit 46is operable to transmit an inbound receive signal 50 to the powergenerating and signal detection module 40. In a passive embodiment ofmultimode RFID tag 38, the RFID reader 14-18 first generates anunmodulated, continuous wave (CW) signal to activate and power the tag.The power generating and signal detection module 40 converts this typeof CW unmodulated inbound receive signal 50 into a supply voltage. Thepower generating circuit signal detection module 40 stores the supplyvoltage and provides it to the other modules for operation.

The RFID reader 14-18 then transmits a modulated, encoded interrogationinbound receive signal 50. The power generating and signal detectionmodule 40 receives the inbound receive signal 50 from the configurablecoupling circuit 46. The power generating and signal detection module 40demodulates the inbound receive signal 50 to recover the encoded data52. Depending on the RFID reader 14-18 and mode of operation, theinbound receive signal 50 may be modulated using Amplitude Shift Keying(ASK) or Phase Shift Keying (PSK) or other type of modulation. In anembodiment, the power generating and signal detection module 40 isoperable to demodulate the inbound receive signal 50 using one or moretypes of demodulation techniques to recover the encoded data 52 from theinbound receive signal 50. The power generating and signal detectionmodule 40 transmits the recovered encoded data 52 to the basebandprocessing module 42.

The baseband processing module 42 receives the encoded data 52 anddecodes the encoded data 52 using one or more protocols. Different dataencoding protocols may be defined for signals in near field mode andsignals in far field mode. For example, in near field mode, a first dataencoding protocol may be used by the baseband processing module 42 fordecoding data while a second data encoding protocol may be used by thebaseband processing module 42 for decoding data in far field mode. Forinstance, Manchester encoding may be used when in near field mode andMiller-modulated subcarrier coding and/or biphase-space encoding may beused when in the far field mode. Alternatively, the baseband processingmodule 42 may use the same data encoding protocol for near field modeand far field mode.

In an embodiment, the baseband processing module 42 is programmed withmultiple encoding protocols to be operable to decode the encoded data 52in accordance with different protocols. Thus, the baseband processingmodule 42 is operable to decode the encoded data 52 using differentencoding protocols when necessary in either near field or far fieldmode. For example, when operating in near field mode, the basebandprocessing module 42 may attempt to decode the encoded data 52 using afirst protocol typical in near field operations, such as Manchestercoding. If such decoding is unsuccessful, the baseband processing moduleis operable to attempt decoding the encoded data 52 with a next protocoluntil the encoded data 52 is decoded. Similarly, when operating in farfield mode, the baseband processing module 42 may attempt to decode theencoded data 52 using a second protocol typical in far field operations,such as Miller-modulated subcarrier coding and biphase-space encoding.If such decoding is unsuccessful, the baseband processing module isoperable to attempt decoding the encoded data 52 with a next protocoluntil the encoded data is decoded.

Once decoded, the baseband processing module 42 processes the decodeddata to determine a command or commands contained therein. The commandmay be to store data, update data, reply with stored data, verifycommand compliance, acknowledgement, change mode of operation, etc. Ifthe command(s) requires a response, the baseband processing module 42determines the response data and encodes the response data into outboundencoded data 54. Preferably, the baseband processing module 42 encodesthe data for the response using the same encoding protocol used todecode the inbound encoded data 52. Once encoded, the basebandprocessing module 42 provides the outbound encoded data 54 to thetransmit section 44. The transmit section 44 receives the outboundencoded data 54 and converts the outbound encoded data 54 into anoutbound transmit signal 56.

The outbound transmit signal 56 is a carrier signal with amplitudemodulation, such as ASK, or phase modulation, such as PSK, or loadmodulation of the carrier signal can be used. The frequency of thecarrier signal in near field mode in one embodiment is a low frequency(LF) or a high frequency (HF) range. In accordance with ISO seriesstandards, such near field ranges are a low frequency at approximately135 KHz or less and a high frequency at approximately at 13.56 MHz. Infar field mode, in an embodiment, the frequency of the carrier signal isin the ultra high frequency range or microwave range. In accordance withISO series standards, such far field ranges are at approximately 2.45GHz frequency, approximately 860 MHZ to 930 MHz ultra high frequency(UHF) range or approximately 433.92 MHz UHF.

In near field mode, the configurable coupling circuit 46 is operable tocouple the transmit section 44 to an inductor in the configurablecoupling circuit 46 to transmit the outbound transmit signal 56 usingelectromagnetic or inductive coupling to an RFID reader 16-18. In farfield mode, the configurable coupling circuit 46 is operable to couplethe transmit section 44 to the antenna section 48, and the multi-modeRFID tag 38 then utilizes a back-scattering RF technology to transmitthe outbound transmit signal 56 to RFID readers 16-18.

FIG. 3 is a block diagram of one embodiment of the configurable couplingcircuit 46. The configurable coupling circuit 46 includes a capacitor C160, an inductor L1 62, and a second capacitor C2 66. In one embodiment,the configurable coupling circuit includes a switch 64. The switch 64 inthis embodiment connects the antenna section 48 and capacitor 66 to theinductor L1 and capacitor C1 in a first position. In a second position,the switch 64 connects the antenna section 48 and capacitor 66 to groundor otherwise isolates the antenna from the inductor L1 and capacitor C1.The switch 64 may be an actuator, a transistor circuit, or otherequivalent device. For an active tag, a battery 41 may power the switch64. For passive tags, an RFID reader 16-18 transmits a continuous wave,unmodulated signal to power the multi-mode RFID tag 38. The multi-modeRFID tag 38 may then use voltage generated from the power generating andsignal detection module 40 to power the switch 64 to change positions.In an alternate embodiment, the multi-mode RFID tag 38 may be configuredprior to provisioning to operate in only near field mode or far fieldmode. For example, the multi-mode RFID tag 38 may be hardwired atmanufacturing to only couple to the antenna section 48 for operation infar field mode or to only couple to the coil antenna 62 to operate innear field mode. In another example, the RFID tag 38 may bepre-programmed to operate only in near field mode or far field modeprior to provisioning.

In far field mode, the antenna 48 and capacitor C2 are coupled toinductor L1 and capacitor C1. Inductor L1 and capacitor C1 are operableas an impedance matching circuit for the antenna 48. The inductor L1provides an inductance value for impedance matching for the antenna 48and the capacitor C1 provides a capacitance value to the impedancematching for the antenna 48. In an embodiment, the capacitor C1 isadjustable or variable, such as a digital switched capacitor, and isoperable to be tuned to provide a desired capacitance value for theimpedance matching in far field mode. Thus, in far field mode, theantenna 48 and the configurable coupling circuit 46 receive the inboundreceive signal 50 and are operable to provide the inbound receive signal50 to the power generating and signal detection module 40.

In near field mode, the switch 64 is open such that the capacitor C2 isfloating or connected to ground. In another embodiment, the multi-modeRFID tag 38 does not include a switch 64 but is hardwired atmanufacturing to isolate the antenna 48 and/or capacitor C2 from theinductor L1. In an alternate embodiment, other devices other than aswitch 64 may be used to isolate the antenna 48 and/or capacitor C2 andthe inductor L1 while the multi-mode RFID tag 38 is in near field mode.

The inductor L1 acts as a coil antenna to provide electromagnetic orinductive coupling with the coil or coils of RFID reader 14-18. Theinductor L1 and the capacitor C1 form a resonant circuit tuned to thetransmission frequency of the RFID reader 14-18. In response to themagnetic field generated by the RFID reader 14-18 coil antenna, thevoltage at the inductor L1 reaches a maximum due to resonance step-up inthe parallel resonant circuit. In an embodiment, the capacitor C1 isadjustable or variable and is operable to be tuned to provideoptimization of the parallel resonant circuit. For example, thecapacitor C1 may be adjusted to provide optimization of at least one ofbandwidth, quality factor, gain and roll-off of the configurablecoupling circuit 46 in the near field mode. Generally, to operate in thenear field mode, the distance between the inductor L1 of the RFID tag 38and the coil antenna of the RFID reader 14-18 must not exceedapproximately λ/2π, so that the inductor L1 is located within themagnetic field created by the coil antenna of the RFID reader 14-18. Innear field mode, the configurable coupling circuit 46 is operable toprovide the inbound receive signal 50 to the power generating and signaldetection module 40.

During transmission, the inductor L1 acts as a coiled antenna thatcreates the magnetic field from current flowing through the inductor L1using the energy provided to the transmit section 44 by the powergenerating and signal detection module 40. Again, in order to receivethe outbound transmit signal 56 in the near field mode, the distancebetween the inductor L1 of the RFID tag 38 and the coil antenna of theRFID reader 14-18 should be equal to or less than approximately λ/2π, sothat the coil antenna of the RFID reader 14-18 is located within themagnetic field created by the inductor L1.

In one embodiment, as explained above with respect to FIG. 2, thebaseband processing module 42 is operable to process commands from anRFID reader 14-18. For example, one command from the RFID reader 14-18may be a mode command to operate the multi-mode RFID tag 38 in nearfield mode or in far field mode. Upon processing such mode command, thebaseband processing module 42 is operable to configure the multi-modeRFID tag 38 to operate in near field more or far field mode. In anotherembodiment, the multi-mode RFID tag may have a preset input that may beset by a user to determine the mode of operation. Thus, uponinstallation of the multi-mode RFID tag in a particular application, theRFID tag may be preset to the mode best suited for such application.

FIG. 4 illustrates another embodiment of a multi-mode RFID tag 68 inaccordance with the present invention. Similarly, to FIGS. 2 and 3, themulti-mode RFID tag 68 in this embodiment includes a power generatingand signal detection module 40, a baseband processing module 42, atransmit section 44, a configurable coupling circuit 46, and an antennasection 48. In addition, a switch 70 and load resistance Zm areconnected between the transmit section and configurable couplingcircuit. In operation, the switching on and off of the load resistanceZm at the inductor L1, e.g. the coil antenna in the near field mode,effects voltage changes at the RFID reader's coil antenna and thus hasthe effect of an amplitude modulation of the RFID reader's antennavoltage by the multi-mode RFID tag 38. By switching on and off of theload resistance Zm in response to the outbound encoded data 54, thetransmit section 44 is operable to transfer the data from the RFID tagto the RFID reader with load modulation. Similarly, the switch 70 andload resistance Zm can modulate the RF backscatter signal from thetransmit section 44 to modulate the reflected RF outbound transmitsignal 56 in far field mode. Thus, the switch 70 and load resistance Zmprovide an efficient modulation of the outbound transmit signal 56 forthe multi-mode RFID tag 38.

The embodiment 4 illustrates a passive RFID multi-mode tag 38. Inanother embodiment shown in FIG. 2, the multi-mode tag 38 may also bedesigned as an active tag by including a battery 41 to provide the powerto operate the RFID tag 38. With active tag design, the power generatingcircuit may not be necessary and an RFID reader 14-18 does not need totransmit a CW, unmodulated signal to power the RFID tag 38 beforecommunicating with the RFID tag 38. In addition, the battery 41 wouldallow the RFID tag 38 to switch between near field mode and far fieldmode in order to detect signals from an RFID reader 14-18 withoutwaiting for a power signal and command from an RFID reader 14-18. Thedisadvantage of active tags with a battery is the shorter duration oflife of the tag. The tag would become inoperable when the battery losesits charge. However, an active multi-mode RFID tag 38 may be optimal forhigher processing applications or applications that only need certainduration, e.g. tags for perishable items.

FIG. 5 illustrates a schematic block diagram of the inductor L1 62 inone embodiment of the multimode RFID tag 38 in accordance with thepresent invention. In this embodiment, the inductor L1 in theconfigurable coupling circuit 46 operates in the ultra high frequency(e.g., UHF) range in near field mode. Due to higher frequencies, thecoils of the inductor L1 can be much smaller sized coils and can beintegrated on chip with other modules of the multi-mode RFID tag 38. Asshown in FIG. 5, the inductor L1 62 has a radius r₂; the coil antenna 80of the RFID reader 14-18 has a radius r₁; and the distance between theinductor L1 and the coil antenna 80 equals distance d. In thisembodiment, with reference to FIG. 5, the magnetic field M₁₂ between thecoil antenna 80 of the RFID reader 14-18 and the inductor L1 of the RFIDtag 38 is:

$M_{12} = \frac{\mu_{0} \cdot \pi \cdot N_{1} \cdot N_{2} \cdot r_{1}^{2} \cdot r_{2}^{2}}{2\sqrt{\left( {d^{2} + r_{1}^{2}} \right)^{3}}}$

wherein μ₀ is the permeability of space. The inductance L_(tag) and Qfactor of the tag Q_(tag) can be determined from:

L_(TAG) ≅ μ₀ ⋅ N² ⋅ r_(av) ⋅ ln (2r_(av)/a)$Q_{TAG} = {\frac{\omega_{0} \cdot L}{r_{series}} \propto \omega_{0}}$

For example, for one embodiment of a multi-mode RFID tag 38 operating innear field mode in UHF range at approximately 900 MHz, the L_(tag)equals approximately 56.6 nH and Q_(tag) equals approximately 4.9.

FIG. 6 illustrates the range between the RFID tag 38 and the RFID reader14-18 in the UHF near field mode assuming the embodiment of FIG. 5. Asseen in FIG. 6, the range is limited by the transmit power of the tag.For example:

${Z_{12}\left( \omega_{0} \right)} = {\frac{V_{2}}{I_{1}} = {\omega_{0}M_{12}Q_{2}}}$Δ Z₁₁(ω₀) ∝ ω₀² ⋅ M₁₂² ⋅ Q₂

and assuming the maximum transmit current of the tag is 500 mA, then therange is approximately 5 mm with a −55 dBV minimum receive signal, thetag's minimum voltage is 0.25 volts, and a 60 dB blocker to signalratio. Note that the tag's input voltage=I₁*Z₁₂; the reader's minimum RXsignal=0.5*(I₁*ΔZ₁₁)2; and the blocker to signal ratio=Z₁₁/ΔZ₁₁. AManchester coding with data rate of 50 kbps is utilized in thisembodiment.

Though the range of communication is smaller (e.g., <5 mm) in UHF nearfield mode than at lower frequencies (such as HF and LF), such shortrange, UHF near field RFID communications are well suited for near readapplications, such as inventory items, monitory paper authentication,passports, credit cards, etc. The near field UHF operation of the RFIDtag 38 also has more efficient operation near fluids, such as fluidmedication bottles. In addition, the inductor L1 or coil antenna 62 maybe designed sufficiently small to be integrated on chip. By integratingthe RFID tag 38 onto a single integrated circuit, the cost of the RFIDtag 38 can be significantly reduced.

The multi-mode RFID tag 38 thus provides near field and far field modeoperation. In one embodiment the multi-mode RFID tag operates in UHFrange in the near field mode with an integrated on chip inductor or coilantenna. By operating in both near field and far field mode, the RFIDtag provides multi-standard, multi-technology option for use in multipleapplications. As such, the RFID tags are not limited to only near reador far read applications but can be used in both type applications andare operable to be switched from near field mode to far field mode orfrom far field mode to near field mode to accommodate different types ofRFID readers and differing distances between the multi-mode RFID tag andan RFID reader.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “coupled to” and/or “coupling” and/or includes direct couplingbetween items and/or indirect coupling between items via an interveningitem (e.g., an item includes, but is not limited to, a component, anelement, a circuit, and/or a module) where, for indirect coupling, theintervening item does not modify the information of a signal but mayadjust its current level, voltage level, and/or power level. As mayfurther be used herein, inferred coupling (i.e., where one element iscoupled to another element by inference) includes direct and indirectcoupling between two items in the same manner as “coupled to”. As mayeven further be used herein, the term “operable to” indicates that anitem includes one or more of power connections, input(s), output(s),etc., to perform one or more its corresponding functions and may furtherinclude inferred coupling to one or more other items. As may stillfurther be used herein, the term “associated with”, includes directand/or indirect coupling of separate items and/or one item beingembedded within another item. As may be used herein, the term “comparesfavorably”, indicates that a comparison between two or more items,signals, etc., provides a desired relationship. For example, when thedesired relationship is that signal 1 has a greater magnitude thansignal 2, a favorable comparison may be achieved when the magnitude ofsignal 1 is greater than that of signal 2 or when the magnitude ofsignal 2 is less than that of signal 1.

The present invention has also been described above with the aid ofmethod steps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claimed invention.

The present invention has been described above with the aid offunctional building blocks illustrating the performance of certainsignificant functions. The boundaries of these functional buildingblocks have been arbitrarily defined for convenience of description.Alternate boundaries could be defined as long as the certain significantfunctions are appropriately performed. Similarly, flow diagram blocksmay also have been arbitrarily defined herein to illustrate certainsignificant functionality. To the extent used, the flow diagram blockboundaries and sequence could have been defined otherwise and stillperform the certain significant functionality. Such alternatedefinitions of both functional building blocks and flow diagram blocksand sequences are thus within the scope and spirit of the claimedinvention. One of average skill in the art will also recognize that thefunctional building blocks, and other illustrative blocks, modules andcomponents herein, can be implemented as illustrated or by discretecomponents, application specific integrated circuits, processorsexecuting appropriate software and the like or any combination thereof.

1. A multi-mode radio frequency identification (RFID) tag operable in a near field mode and a far field mode, comprises: a transmit section for transmitting an outbound transmit signal, wherein the outbound transmit signal is encoded using a first protocol when in the far field mode and encoded using a second protocol when in the near field mode; and a configurable coupling circuit that couples the transmit section to a first circuit for transmitting the outbound transmit signal as an RF signal in the far field mode and that couples the transmit section to a second circuit for inductive coupling to transmit the outbound transmit signal in the near field mode.
 2. The multi-mode RFID tag of claim 1, wherein the first circuit includes an antenna for transmitting the outbound transmit signal as an RF signal in the far field mode and the second circuit includes an inductor for inductive coupling to an RFID reader when the RFID tag is operating in the near field mode.
 3. The multi-mode RFID tag of claim 2, further comprising: a power generating and signal detection module coupled to the configurable coupling circuit, wherein the power generating and signal detection module converts an inbound receive signal into a supply voltage and recovers encoded data from the inbound receive signal.
 4. The multi-mode RFID tag of claim 3, further comprising: a baseband processing module coupled to: decode the encoded data to produce a decoded signal; process the decoded signal; when the processing of the decoded signal indicates generating a response signal, generate the response signal; and encode the response signal to produce outbound encoded data, wherein the response signal is encoded using the first protocol in far field mode and encoded using the second protocol in near field mode.
 5. The multi-mode RFID tag of claim 4, wherein the transmit section converts the outbound encoded data into the outbound transmit signal.
 6. The multi-mode RFID tag of claim 2, wherein the configurable coupling circuit comprises: a first capacitor coupled to the antenna in the far field mode and coupled to ground in the near field mode; and wherein the inductor provides an inductance value for impedance matching in the far field mode.
 7. The multi-mode RFID tag of claim 2, wherein the configurable coupling circuit comprises: a second capacitor coupled to the inductor to provide a capacitance value to tune the impedance matching for the far field mode and to tune at least one of: bandwidth, quality factor, gain and roll-off of the configurable coupling circuit in the near field mode.
 8. The multi-mode RFID tag of claim 2, wherein the antenna is operable to transmit and receive RF signals in an ultra high frequency (UHF) range in the far field mode.
 9. The multi-mode RFID tag of claim 2, wherein the inductor comprises a coil inductor operable to provide inductive coupling in ultra high frequency (UHF) range in the near field mode.
 10. The multi-mode RFID tag of claim 2, wherein the inductor comprises a coil inductor operable to provide inductive coupling in low frequency (LF) range in the near field mode.
 11. The multi-mode RFID tag of claim 1, wherein the RFID tag is associated with at least one of: an access card, smart card, mobile phone, personal digital assistant, laptop, personal computer, inventory item, pallet, carton, equipment and personnel.
 12. The multi-mode RFID tag of claim 1, wherein the RFID tag is operable to operate in far field mode in response to a first command from an RFID reader and wherein the RFID tag is operable to operate in near field mode in response to a second command from the RFID reader.
 13. A method for operating a multi-mode RFID tag, comprising: when operating in a far field mode, encoding an outbound transmit signal using a first encoding protocol and transmitting the outbound transmit signal as an RF signal; and when operating in a near field mode, encoding the outbound transmit signal using a second encoding protocol and transmitting the outbound transmit signal with inductive coupling.
 14. The method of claim 13, further comprising: when operating in a far field mode: receiving an inbound signal from the RFID reader, recovering an encoded data signal from the inbound signal; decoding the recovered encoded data signal with the first encoding protocol; processing the decoded data signal; generating a response signal to the decoded data signal; and encoding the response signal with the first encoding protocol.
 15. The method of claim 14, further comprising: modulating the response signal encoded with the first encoding protocol onto a carrier signal, wherein the carrier signal is in the ultra-high frequency (UHF) range; and transmitting the modulated carrier signal to the RFID reader using RF coupling.
 16. The method of claim 13, further comprising: when operating in a near field mode: receiving an inbound signal from the RFID reader, recovering an encoded data signal from the inbound signal; decoding the recovered encoded data signal with the second encoding protocol; processing the decoded data signal; generating a response signal to the decoded data signal; and encoding the response signal with the second encoding protocol.
 17. The method of claim 16, further comprising: modulating the response signal onto a carrier signal, wherein the carrier signal is in the ultra-high frequency (UHF) range; and transmitting the carrier signal to the RFID reader using inductive coupling
 18. The method of claim 13, further comprising: converting the inbound receive signal from the RFID reader into a supply voltage to operate the RFID tag in both near field mode and far field mode.
 19. The method of claim 13, wherein the outbound transmit signal is in an ultra high frequency (UHF) range in both far field mode and near field mode.
 20. The method of claim 13, wherein the outbound transmit signal is in an ultra high frequency (UHF) range in far field mode and in a low frequency (LF) range in the near field mode. 